Developments in recent years of digitization techniques are so remarkable that it becomes possible for image signals corresponding to a movie in its entirety to be recorded as digital information in a single optical disk. One of reasons why it becomes possible to store such a massive amount of digital information in a single optical disk can be shown as a progress of optical disk recording media. Optical disks include magneto optic recording and phase change types both of which use an amorphous thin film low in phase transformation temperature, which consists of a compound of rare earth and transition metal elements, to make high density and high efficiency recording possible (see Nonpatent Reference 1).
However, there is the problem that rare earth elements are low in ore reserves and therefore high in cost. There is also the problem that an amorphous thin film is complex in composition and, if it is continued that data are repeatedly written and erased on it over a prolonged time period, tends to change its composition so that it can no longer allow its writing and erasing. The film has further the problem that in its magnetizing it needs to be made amorphous upon rearranging the crystallographic structure over its entire material in a recording region and entails large amount of energy consumed to this end.
Further, in a process of magnetically recording on a magnetic tape or a hard disk where several magnetic fine particles constitute a storage area, the recording density is limited depending on the size of the magnetic fine particles. There is a limit in making the particles finer and it is difficult to increase the recording density higher than the existing limit.
Moreover, where there is no end to the demands for the rise in recording density, attempts to utilize near-field optical techniques so to record beyond the diffraction limit of read and write laser light have begun (see Nonpatent Reference 2). To enhance the recording density, however, it is indispensable and essential not only to improve the recording method but also to develop a material based on new operating principles that can withstand the recording density.
Furthermore, it is possible to utilize nonvolatile phase change magnetic materials not only for memory applications but also, e.g., as a material for forming magnetic latent images in a copying machine using magnetic toner as ink. For example, a nonvolatile phase change magnetic material can be applied to a drum surface, which is irradiated with a laser beam to cause a nonvolatile phase change and form a magnetic latent image to which the magnetic toner is adhered for printing on paper and thereby copying. While a ferromagnetic film has hitherto been used as the magnetic latent image material for magnetic recording to form magnetic latent images by magnetizing the ferromagnetic film with a magnetic head, the recording density is limited by the size of magnetic fine particles and the resolution of images is now approaching its limit and, as a result, a magnetic material capable of recording a image of high definition is being sought.